This invention relates to a sealing gasket, particularly to a cylinder head gasket for an internal combustion engine. The sealing gasket comprises a soft-material plate which may be reinforced by metal inserts and which has openings for the mounting bolts, the engine coolant, the lubricant and the combustion chambers. At least one of the openings in the sealing gasket is framed by a metallic border flange formed of two superposed, bent sheet metal members which have a U cross section.
The gasket openings associated with the combustion chambers of the engine are preferably provided with metallic border flanges as outlined above, because in the zones of such openings the stress exerted on the gasket by the hot combustion gases is at a maximum. Such metallic border flanges are formed, as a rule, of a sheet metal member bent over the edge of the gasket opening onto opposite sides of the gasket, whereby the border flanges have a U-shaped cross section. Apart from a particular protective effect in the framed zone of the gasket, there is obtained a sealing pressure which is increased due to the thickness of the border flange and thus superior sealing properties are ensured.
In high-load internal combustion engines, however, the above-outlined measures concerning the sealing gasket are usually not sufficient because of the high compression. Since the thickness of the sheet metal from which the border flanges are made cannot be increased at will, the corresponding gasket zones have been provided with additional overlays, or additional insert rings are placed under or on the border flanges. In accordance with a solution disclosed in German Pat. No. 1,525,811, the ends of the border flange legs are folded over, so that an additional sealing pressure is obtained in a simple manner, while, at the same time, a barrier effect is achieved against the pressure-caused flow of the soft material of the gasket. In such a case, however, the sealing starts only at the ends of the border flange legs, so that the hot combustion gases may flow in the gap up to the folded-over legs and in their path they may destroy the soft material of the gasket as well as the sheet metal of the border flange.
German Laid-Open Application (Offenlegungsschrift) No. 2,028,498 proposes to superpose a second border flange sheet of U-shaped cross section on the usual border flange. The second border flange is significantly thicker than the usual border flange it surrounds, for the purpose of achieving a particular protective effect. Such a measure, however, requires the provision of particular recesses in the engine block and the cylinder head for accommodating the thick border flanges; the recesses have to be dimensioned very accurately. Consequently, such a gasket cannot find universal application.